1. Field of the Invention
The present invention generally relates to methods for weld repairing metal alloys, particularly those suitable for use in the high temperature environment of a gas turbine engine. More particularly, this invention relates to a method of performing a controlled weld repair of a defect in a component formed of such an alloy, wherein the method minimizes melting of the alloy with a filler material used to repair the defect.
2. Description of the Related Art
Hot section components of gas turbine engines, such as blades (buckets), vanes (nozzles) and combustors, are typically formed of nickel, cobalt and iron-base superalloys characterized by desirable mechanical properties at turbine operating temperatures. These components are typically used in cast form, and as a result can have point defects, e.g., ceramic inclusions, pores, etc., as well as small linear defects that require repair. Various welding techniques have been developed that are capable of repairing these defects, including tungsten inert gas (TIG) and plasma transferred arc (PTA) welding processes that must be carefully carried out to achieve acceptable welding yields and ensure that the mechanical properties of the superalloy are maintained. Use is particularly made of relatively simple manual repair methods, such as TIG with a filler material, which can be readily implemented by casting suppliers.
As known in the art, welding involves local melting and resolidification. To prevent cracking, an alloy being repaired by welding must be sufficiently ductile to accommodate the thermal strains that develop during welding. However, temperature resistant materials of the type used in gas turbine engines are inherently resistant to deformation, such that filler materials formed of the same alloy as the component being repaired are difficult to use at room temperature. As a result, alloys more ductile than the parent alloy are frequently used to repair superalloy components. A difficulty encountered when using a ductile filler to repair a superalloy component is that the ratio of filler to parent metal is hard to control in manual processes such as TIG. Frequently, TIG welds of superalloys and other alloys that are difficult to weld will experience cracking in the root passes of the weld due to excessive melting of the parent metal into the molten pool of filler metal.
In view of the above, it would be desirable if a method were available for repairing high-temperature metal alloys, by which excessive melting of the parent metal and mixing with the filler metal could be minimized.